


Illegal Lover

by J_st_patricks_daY28



Category: Stranger Things (TV 2016)
Genre: Aftercare, Alternate Universe, Bathroom Sex, Blow Jobs, Blow Jobs in a Car, Bottom Seven | Kate Hopper, Choking, Consensual Somnophilia, Consensual Underage Sex, Daddy Kink, Dom/sub, F/M, Fluff and Smut, Grinding, Hair-pulling, Oral Sex, Pet Names, Praise Kink, Roleswap, Secret Relationship, Shotgunning, Soft Billy Hargrove, Somnophilia, Step-Sibling Incest, Subdrop, Teen Romance, Thighs, Top Billy Hargrove, Vaginal Fingering, Vaginal Sex
Language: English
Status: In-Progress
Published: 2020-07-02
Updated: 2020-09-03
Packaged: 2021-03-04 18:35:08
Rating: Explicit
Warnings: Underage
Chapters: 3
Words: 4,538
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25040989
Author URL: https://archiveofourown.org/users/J_st_patricks_daY28/pseuds/J_st_patricks_daY28
Summary: "It's Kate.""Sorry?""Nobody calls me Katherine, It's Kate."ORThe Step-Siblings AU no one asked for.
Relationships: Billy Hargrove/Seven | Kate Hopper
Kudos: 22





	1. Kool Kate

"To slay the dragon, use the magic sword."

"Oh, Jesus! I'm in uncharted territory here, guys."

"Down! Down! Down!"

"I'm going! I'm going! I'm going!"

The cartoon woman known as Princess Daphne gasped as the game picked up speed. The boys yelled over one another as they cheered Dustin on while he played.

"Okay. Shut up. Shut up. Shut up!"

Dustin slammed his hands down on the buttons, but then the disappointing sounds from the machine indicated he had lost.

"No, no, no! I hate this overpriced bullshit! Son of a bitch! piece of shit!"

The screen returned to the original title screen, inviting its next player. Lucas started to gloat at Dustin.

"You're just not nimble enough. But you'll get there one day. But until then, Princess Daphne is still mine."

"You know what? Whatever. I'm still top on Centipede and Dig Dug."

"You sure about that?"

The boys turned their heads to see one of the employees, Keith. He was standing with a bag of cheese puffs and an awkward smirk.

"Sure about what?"

Keith only smiled and took a large rather obnoxious bite out of a cheese puff.

"You're kidding me, no, no, no, no, no."

Dustin broke out into a panicked sprint and the others quickly followed suit, curious to see the outcome.

"Move! Move! No, no, no, no, no. No! No! No!"

The boys zeroed in on the Dig Dug screen where sure enough, Dustin held second place to someone named KOOL KATE who held an insanely good score.

"751,300 points!"

"That's impossible."

"Who's Kool Kate?"

"Better than you."

"Is it you?" 

Keith scoffed. "You know I despise Dig Dug."

"Then who is it?"

"Yeah, spill it, Keith."

"You want information, then I need something in return," He smirked and looked at Mike.

"No. No, no, no. No way. You're not getting a date with her."

"Mike, come on. Just get him the date."

"I'm not prostituting my sister!"

"But it's for a good cause."

"No, don't get him the date. Know what? He's going to spread his nasty-ass rash to your whole family."

"Acne isn't a rash and it isn't contagious you pre-pubescent wastoid."

"Oh, I'm a wastoid? She wouldn't go out on a date with you. You make, like, what? $2.50 an hour?"

"Nice perm."

"Gonna make fun of my hair?"

As the boys continued their argument Will looked over his shoulder as he heard something outside the archade. He turns to alert his friends but they're nowhere in sight.


	2. Rock You Like A Hurricane

**Summary for the Chapter:**

> Hawkins High has some new students.

“Meet the human brain, I know. I know, it doesn’t look like much. A little gross even, right? But consider this. There are a hundred billion cells inside of this miracle of evolution. All working as one. No, I did not misspeak. I did not stutter. A hundred billion.”

The abrupt sound of the door opening drew everyone’s attention to the front of the classroom. The principal walked in with the new girl. She had medium length hair that was as black as coal.

“Ah, this must be our new student.”

“Indeed, it is. All yours.” With that, the principal left the classroom.

The new girl attempted to rush past and find a seat, but Mr Clarke stopped her.

“All right. Hold up. You don’t get away that easy. Come on up. Don’t be shy.”

She rolled her eyes as she backed up to the front of the class and faced her new peers.

“Dustin drum roll.”

Dustin marked his spot with his pencil and closed his textbook before he started drumming his palm on the hardcover.

“Class, please welcome, all the way from sunny California, the latest passenger to join us on our curiosity voyage, Katherine.”

“It’s Kate.”

“Sorry?”

“Nobody calls me Katherine. It’s Kate.”

The boys looked at each other, thinking the same thing.

“Kool Kate,” Lucas whispered.

“Well, all aboard Kate.”

Kate took a seat at the back of the class. She leaned back and crossed her arms, obviously still uncomfortable from the sudden spotlight. She frowned when she noticed that the guys were staring at her.

* * *

The boys stood in the small baseball dugout, watching Kate. She was riding her skateboard all around the campus.

“There’s no way that’s Kool Kate,” Mike stated matter of factly.

“Yeah, girls don’t play video games.” Will agreed.

“And even if they did you can’t get 750,000 points on Dig Dug. I mean it’s impossible.”

“But her name is Kate,” Lucas argued.

“So what?”

“So, how many Kates do you know?”

“I don’t know.”

“Zero, that’s how many.”

“Yeah, and she shows up at school the day after someone with her same name breaks our top score. I mean, are you kidding me?” Dustin chimed in.

“Exactly! So, she’s got to be Kool Kate. She’s got to be.”

“Plus, she skateboards, so she’s pretty awesome,” Dustin said, much to the dismay of Mike.

“Awesome? You haven’t even spoken a word to her!”

“I don’t have to; I mean look at her. Shit, I’ve lost the target.”

“There,” Will said, pointing to the back entrance of the school.

Kate walked up the steps with her skateboard in her hand. She dropped a crumpled piece of paper into the trash before heading inside. The boys looked at each other before running towards the trash. After some digging Dustin found the piece of paper. The other boys stood next to him and read the not in unison.

**Stops spying on me CREEPS**

“Well, shit.” Dustin sighed.

* * *

Kate slid her skateboard into her locker before she slammed the blue metal door shut and reset the keypad. She then turned tail and started walking down the hallway. Nobody uses the girl’s bathroom on the far-right end of the gym. There are rumours about it being haunted or whatever. Kate knows it’s not true. it’s just that the prissy popular girls are scared of spiders.

The dark-haired teen threw a look over her shoulder to make sure there was no one around before pushing open the door and slipping inside. Before she could turn around fully someone grabbed her by her shoulders and slammed her against the wall before a pair of soft lips were on hers.

Kate didn’t struggle or squirm. Because she knew who it was. She just sighed through her nose and kissed back. Lips moving in sync with the occasional bite from canine-like teeth. After a few minutes, Kate broke off because she felt like her lungs were about to collapse. She panted heavily; her face felt as if it was on fire.

She chuckled and looked into her stepbrother’s ocean eyes. They were burning with lust. “fancy seeing you here Billy.”

Billy smirked and kissed her cheek. “I missed you.”

“Why? Are the girls all over you?”

“Yeah, I haven’t been able to stop thinking about you, Katherine.” He said, ghosting his lips over hers.

“Don’t call me that.” She said, gripping his bicep as a warning. Most people think that Kate is more bark than bite but that’s not the case at all. Her bark can get intense, but her bite’s a hell of a lot worse.

She reached up and tried to pull him down for another kiss. She’s not tall enough to get there on her own. She’s only 5’2 and he’s 5’10. Even if she rocked up onto her tiptoes, she could reach his jawline at most. Billy grabbed her ass and squeezed. Smacked it. She bit her lip because she didn’t want to hand over the ropes yet.

“You’re such a horny slut, you can’t wait until after school?”

“You’re the one who told me to meet you here, Billy. I was tempted to meet up with one of the seniors. He was cute and shy, but he promised me a good time.” Kate said, smirking at him.

Her comment made him growl in jealousy. He attached his lips to her neck. Pressing kisses to her lightly tanned skin until his teeth found a spot to suck a deep purple bruise into her neck. Kate shuddered and gasped. Her eyes fell shut as she finally gave him the ropes.

Billy pulled off her neck, satisfied with the hickey he had left behind. “All mine. As it should be.”

“And always will be,” Kate said, trailing her hands down his chest.

He smiled softly. She always knew how to soften him up. In more ways than one. Billy leaned his head to the right just a bit and kisses her. Their kiss is soft, a little wet. He peeked through his lashes and saw that Kate had her eyes closed.

She kissed so sweetly, hands resting on his chest and sliding up to wrap around Billy's shoulders. Kate bit down on his bottom lip, a prick of pain soothed away by her slick tongue. Billy groans and broke away from her lips. He got on his knees and pulled her jeans down after he popped open the button and undid the zipper.

She’s soaked through, the wet fabric clinging to her clit. Billy thought about just pushing her panties aside and pressing into her. Kate deserved better, though. He pressed the heel of his palm against the seam of the cotton, listened to her whine at the friction on her clit.

“More, please!” Kate shuddered in his touch. If Billy had known this is what it took to get her to listen, he would have done this years ago when she couldn’t stop staring at him weightlifting in the living room.

“Shh, I’ve got you, baby girl,” Billy hushed her, stroking over her wetness as he mouthed at her waist. He pulled her panties down and placed his lips on her clit. She moaned, nails digging into his shoulders. Her breathing became heavier the longer she received the hot, wet feeling of him greedily devouring her.

Billy pushed two fingers in, Kate rolled her hips down, she was so wet she took his fingers with no problem and a breathless moan. He devoured her, getting addicted to the taste of her as he fingered her. His thumb rolled over her clit.

“Fuck,” Kate swore so he did it again. He buried his tongue into her clit as deep as he could, she fell apart on his fingers and his mouth and came with a moan that rang in his ears. Her face flushed, mouth open as she caught her breath.

Billy slowly withdrew and licked his fingers clean, staring at her the entire time. He then pulled her panties back up and fixed her jeans, adoring the way she would twitch from the aftershocks of her orgasm. He lit a cigarette and leaned against the wall, draping an arm over her shoulders. Kate plucked the cigarette from between his fingers and took a drag, exhaling a smooth cloud, and give it back. Billy smoked slow, holding Kate, with her head resting against his chest.

Once he finished, he flicked the cigarette to the floor and stomped on it to extinguish it. He leaned down and kissed her, his kiss tasted of nicotine. “I’ll see you later.”

Kate smiled and gave him a wink. Billy smacked her ass when she turned to leave. She flipped him off, her sassiness coming back to the surface. She pulled the door open and was out of sight.


	3. Trick Or Treat, Freak

**Summary for the Chapter:**

> October 31, 1984

_Three to the right, four to the left._

Kate let her locker swing open and put her books on the small shelf in the locker space. Dustin cleared his throat to grab the dark-haired teen’s attention. “Hi, Kate, I’m Dustin and this is…”

“Lucas.”

“Yeah, I know. The stalkers.”

The two boys looked at each other and stumbled over their words to come up with an explanation. “Uh… actually we weren’t stalking you.”

“No, we- we were just concerned because you know you’re new and all.”

“Ye-Yeah for your safety.”

“Mmm, there are a lot of bullies here.”

“So many bullies, I mean it’s crazy.”

“Is that why you’re wearing proton packs?”

“Well these don’t function, but,” Dustin reached behind him and grabbed his handmade ghostbusters trap. “I do have this handy dandy little trap here, and look it even opens and closes. Look, look, voila. Cool right? No? Okay but uh we were talking last night and you’re new here, so you probably don’t have any friends to take you trick-or-treating, and you’re scared of bullies, so we were thinking that it would be okay if you come with us.”

“‘It’d be okay’?”

“Yeah. Our party’s a democracy, and the majority voted that you could come.”

“I didn’t realize that it was such an honour to go trick-or-treating with you.” Kate said with a fake smile plastered on her face. She was annoyed that these boys were wasting her time. She wanted this pointless conversation to be over so she could go home with Billy.

“Yeah, I mean, we know where to get the full-sized candy bars. We figure you’d want in.”

“That’s presumptuous of you.” Her eyes squinted ever so slightly.

“…Yeah, totally, so uh, you’ll come?”

Kate rolled her eyes, slamming her locker with a scoff and walked away, leaving Dustin and Lucas.

“We’re meeting at the Maple Street cul-de-sac at 7:00. That’s 7:00 on the dot.” Dustin called out as she turned the corner to exit the school. “‘Presumptuous’ that’s a good thing, right?”

Lucas sighed and turned tail, walking down the hall. Dustin looked at his friend confused and hurried after him. “Is it bad? Lucas, is it bad? Lucas? Son of a bitch, Lucas. is it bad?”

* * *

Kate skated across the carpark towards her stepbrother’s blue Camaro. She knew he was gonna say something about her being late. But it wasn’t her fault those boys wasted her time. Said boy was leaning against the side of the hood and smoking.

“You’re late again, Katie.”

“Sorry Billy, I had to get catch up homework.” She lied, getting off her board and picking it up.

“It’s okay baby girl. Just try to not be late again. You know I don’t like waiting.” He propped her chin up a little with his index finger and dragged his thumb over her bottom lip before walking around to the driver’s side. Kate opened the passenger door and climbed in. Putting her skateboard and her backpack in the back seat. The song Wango Tango blasted on the radio as the car sped down the road.

“God, this place is such a shithole.” Billy scoffed; his comment grabbed Kate’s full attention.

“It’s not that bad.”

“No?” He looked at her and rolled down the window. He took a deep breath and pulled his nose. “You smell that, Kate? That’s actually shit. Cow shit.”

“I don’t see any cows, Billy.” She stated, rolling the window back up.

“Clearly you haven’t the high-school girls.” He looked over at her again before back at the road. “So, what, you like it here now?”

“What? No,” She said defensively.

“Then why are you defending it?”

“I’m not.” She stated, lowering the defensive tone in her voice and looking at him.

“Sure, sounds like it.” He said calmly.

Whenever Billy got calm like this, it was a good thing. It usually meant he was going to give her a little something. She never knew what that something was though. Her heart quickened a little and she felt her face heat up. “It’s just we’re stuck here so…”

“Hmm. You’re right. We’re stuck here,” Billy turned his head and looked at her again. This time he eyed her up and down. He licked his lips, took his hand from the leather steering wheel and rested it on her thigh, lightly gripping it. “And whose fault is that?”

His attention went back to the road. Kate looked down at his hand and discreetly bit her lip. She knew how to poke at him to get him riled up. “Yours.”

“What’d you say, Katie?” He looked at her, back at the road then at her again and licked his lips.

“Nothing, Daddy.”

“Did you say it’s my fault?” He glided his hand up and started rubbing her through her jeans.

“No, of course not.” She said, her breathing became heavier at the friction his fingers were giving her.

“You know whose fault it is. Say it.”

Kate whimpered, letting her eyes close. Her mind fogged over, she started to feel lightheaded. She didn’t want to give him what he wants to hear yet, so she kept silent.

“Kate…” He said lowly, drawing out her name. “Say it.” He growled, pressing his fingers hard against her clothed heat. He knew all of her soft spots, so he knew where to touch her to get what he wants.

She finally gave in, a sharp gasp escaped from her throat and she told him what he wanted to hear. “Mine. It’s my fault.”

“Good girl.” Billy praised and slipped his hand into her jeans, fingering her as a reward. All of the beautiful noises that Kate made went straight to his cock. Kate clenched around his fingers as he thrusted them at a deep, steady pace.

Her body hummed it’s approval and her lower abdomen started tightening. Just when she felt herself begin to topple over the edge, he removed his fingers. She looked at him and huffed, clearly pissed off that he denied her orgasm. “Billy what the fuck was that for?”

The blonde chuckled, meeting her gaze. “You don’t get to cum until I say so Katie.”

Kate groaned in annoyance and crossed her arms, slumping back in her seat. She was tempted to touch herself, but she decided not to and be a good girl, knowing he’d reward her. His foot stomped on the gas and the car went faster than before. Billy threw his hands on the wheel to every beat of the song. He shifted in his seat as his erection pushed against his jeans. “You want to make Daddy feel good, Doll?”

“Obviously.” Kate was horny, desperate and fussy from her denied orgasm. She needed something to satisfy her for the rest of the car ride. If she was irritated when he fucks her when they got home, he wouldn’t like it.

Billy unzipped his jeans and got his cock out, the tip leaking pre-cum. “Hair back before you get to suck me off, doll. You know the rules.”

“Fine.” Kate huffed but obeyed, tying her dark hair back into a low ponytail. Billy grabbed the back of her neck and pulled her down to his crotch, she took him all in one go. She gagged when his tip hit the back of her throat. Her moans sent vibrations down his cock, earning a deep groan from him and a harsh tug on her hair. “Fuck, that’s it Katie, good girl. You love Daddy’s cock, don’t you?”

Kate could only moan in reply. Tears swelled in her eyes and she felt her chest starting to burn. She was running out of oxygen. She squeezed his thigh as an indicator that she needed to come up for air.

“Breathe through your nose like I taught you Baby, you can take it.” Billy kept her down by his firm but gentle hold on the back of her neck.

Kate let her tears fall and did as she was told, taking deep breaths through her nose. Her moans and whines muffled around his cock. She whimpered and he tugged on her hair again, he moaned deeply, and he came into her eagerly sucking mouth. Billy kept a firm hand on the back of her neck, so she stayed where she was and swallowed every last drop of him. She gagged and gripped harshly at his thigh.

“That’s it,” He said. “Take me in, Baby girl.”

Kate’s posture relaxed, she licked and swallowed until he released his hold on her and gently pulled her back up. She’s breathless and trembling. She slumped back into her seat; black spots splattered like paint on a canvas across her vision. She felt stimulated and lightheaded. Billy tucked himself back into his boxers and zipped his jeans up.

Kate let her hair down and stared out the window, her lids getting heavier by the minute. When Billy looked over at her she was fast asleep. He chuckled softly and reached over to hold her hand. “Cutie.”

* * *

Once they arrived back at Cherry Lane Billy killed the ignition and got out of the car. He went to the passenger side and carried Kate inside. Susan and Neil weren’t home yet, fortunately. He gently laid her down on his bed and closed the door, locking the handle. Better be safe than sorry.

Billy climbed on top of her and looked down at her. So _beautiful_ and _vulnerable_. He striped her of her clothes and let his eyes drink it all in. Kate shifted comfortably, a small moan escaping her lips from his fingers exploring her body. She smiled softly still asleep, but she knew it was Billy. He smirked and kissed her every inch of her skin. He trailed his hand in between her legs and slipped two fingers into her. She moaned softly and arched into his fingers.

“Daddy I need more,” Kate begged, “Please, please give me more.”

The fact she was still able to communicate while in deep sleep made Billy so hard it hurt. He palmed his cock through his jeans, trying to slow his breathing as he counted back from ten before stripping off his clothes.

Billy crawled back in between Kate’s thighs and laid himself over her, pushing in without even a reflex of resistance, Billy was caught by just how completely vulnerable Kate has let herself be for him. How much trust Kate placed in him in that moment, absolutely submitting the care of her body over to Billy and Billy felt protective and proud. He moaned into the crook of Kate’s neck as he rocked into her.

A little while later, Kate came to with a soft gasp. The feeling of Billy’s lips on her neck and his deep gentle thrusts flowed her senses without warning. She gripped his bicep and choked out a desperate whine. “Daddy.”

Billy peppered soft kisses on Kate’s jaw. “You back with me Baby girl?”

“Yeah. Ngh, feels so good. Need more.” Her speech is sleep slurred, but he knew exactly what she wanted.

“Fuck, you’re gorgeous,” Billy moaned. He wrapped his hand around Kate’s throat and choked her - not tight enough to cut off her air supply though. “God, I’m so fucking lucky that you’re mine, kitten. Such a pretty little slut, and all for me.”

Kate whimpered, everything felt so good, and her body was desperate for release. It was ecstasy and torture at the same time.

“Love being yours,” Kate panted, reaching out for Billy. “Love when you take what’s yours.”

“I know you do, Princess,” Billy grinned darkly. “You love being daddy’s little toy. You want daddy to show you who you belong to? You want Daddy to fill you with his cum? Don’t want you forgetting whose slut you are, now do we?”

“Fuck, Daddy, please come in me. Need your cum so bad, please use me, please fill me up.” Kate moaned submissively and clenched around Billy’s cock.

“Fuck,” Billy grunted, holding both of Kate’s hips in a tight possessive grip as he fucked her, his thrusts becoming faster, sloppier, more desperate. “Gonna cum in you Baby. Gonna get you nice and messy so everyone will know what a little slut you are for me.” His words sent Kate straight over the edge. She arched and came with Billy’s name on her lips.

“Daddy,” Kate whimpered, her voice shaking. It felt so good just to say it, and she knew it was what Billy needed to hear to push him over the edge. “ _Fuck_ , Daddy, please, please cum in me.”

“Fuck, I’m coming, Baby,” Billy panted and filled her up. He held Kate’s hips as he rode out their highs.

Kate sobbed as she came down, every nerve in her body tingling in the aftermath. She was so physically, mentally, and emotionally overwhelmed; it was the best thing she’d ever felt.

Before she could fully process all the pleasure he was feeling, Billy’s lips were on her heated cheeks, his fingers running through Kate’s hair. He was whispering sweet praises in her ear and wiping away her tears, bringing her back down. “I’m right here, angel. You did so good for me. You’re such a good girl for me, I love you so much. You make Daddy feel so good, sweetheart.”

Kate let out another sob and gripped lightly at his bicep. Billy kissed her forehead and rubbed her hips with his fingers. “Hey, it’s okay, baby. Daddy’s right here, it’s okay.”

Billy pressed all the love and adoration he could fit into one kiss to Kate’s salty, trembling lips. Kate sighed contently when he pulled away, the kiss clearing the fog in her mind. Kate flipped them over and moved south between his thighs.

Billy lifted himself up, supporting himself on his elbows. “Katie what are you doing?”

She looked up at him with a lustful smirk. “You made me come five times today. I can’t have you missing out.”

Billy spread his legs in invitation and rested a hand on the back of her head, puts the other behind his head just to show off his biceps. His cock flushed and somehow still hard. Kate stroked it, rubbed her thumb over the slit to gather wetness. She leaned over, one hand on his thigh as she takes the head in her mouth.

Billy’s head thumped back into his pillow at the feeling of wet and heat, the feeling of him resting flat of her tongue. She sucked gently, tonguing at the slit before taking more in. Billy’s eyes opened - he isn’t sure when he closed them - and watched her cheeks hollow.

She looked up at him, a quick glance through her lashes. Kate’s brown eyes were wet and she’s only halfway down. Billy’s hand on her head rested there, playing with the fine strands of her hair. She stroked him a few more times, twisting her wrist on the upstroke, before her hand resumed stroking what she couldn’t fit in her mouth.

“Oh fuck,” Billy groaned as he pushed into the tight heat of her throat. Kate hummed as she bobbed her head. It’s over in a matter of minutes, Billy wasn’t too fond. He told himself it’s because he hadn’t gotten laid in a while. Which was a blatant lie. It was because that Kate was sucking him off like a champ. He spilled into her mouth and she swallowed it before she pulled out with his dick spit-wet and going soft.

Billy panted heavily as she sat up to redress herself. Once he got his breath back, he put his clothes back on, wrapping an arm around her as she curled up against his chest. His fingers tracing shapes on her back through the fabric of her shirt. She giggled softly and pressed a soft kiss to his neck before closing her eyes. “I love you, Billy.”

“I love you too, Baby Doll.”


End file.
